Glow discharge in gases, also known as cold cathode discharge, is widely used in a variety of devices for such applications as advertising, illumination, and decoration. This technology is also useful for a variety of other applications, including materials processing. Some common examples of gas discharge devices are neon signs and gas lasers.
Gases able to sustain glow discharges, including but not limited to neon, are well known in the art. A gas discharge is generated when sufficient electrical current flows between the cathode and the anode in a chamber, known as a discharge tube or plasma reactor, that is filled with a suitable reactive gas, such as neon. If the cathode is capable of producing the discharge without the application of heat, the cathode is known as a cold cathode.
In order to supply the current flow necessary to generate the glow discharge, a voltage is applied between the cathode and the anode from an external power source. A major drawback to the technology is that very high operating voltages are required. Depending on the geometrical dimensions of the enclosure and the nature of the filling gas, operating voltages up to and exceeding 15 kV may be required to generate a glow discharge in the gas.
Because of the high voltages required to generate a glow discharge, one of the key design parameters for gas discharge devices is aimed at producing the highest possible glow discharge current while minimizing the required operating voltage. The operating voltage is proportional to the electron work function of the material comprising the cathode, and inversely proportional to the cathode's surface area. Thus, for a given cathode material, the operating voltage can be reduced by increasing the surface area of the cathode. The cathode's surface area may be increased simply by increasing the physical dimensions of the cathode, but because the cathode must be contained within the discharge tube, this would require increasing the physical size of the discharge tube to accommodate the larger cathode. This is an undesirable result in many applications.
Hence, a heretofore unaddressed need exists in the industry for a gas discharge device that can be operated at a lower voltage than presently available devices without increasing the physical size of the device.